124 EXPERIMENT STATION. [Jan. 



Supplementary Notes. — Koettstorfer expresses the acidity 

 by the cubic centimeter of N / 1 potassium hydrate required for 

 100 grams of fat as '' degrees of acidity." Stockmeier reports 

 " degrees of rancidity " in the same manner. N/10 alkali and 

 10 grams of fat are, however, more convenient quantities with 

 which to work. 



1° rancidity = .56158 acid number. 

 1° acid number = 1 . 78009° rancidity. 



Rosaniline dev^ops with free fatty acids a red color due to the 

 formation of rosaniline oleate, and is known as the Jacobsen 

 test. 



The acid number of oils and fats varies with the purity, age 

 and the amount of hydrolysis and of oxidation they have under- 

 gone. Contact with fermenting or decaying matter tends to 

 rapidly increase the amount. Rancidity develops more readily 

 in liquid oils in which olein predominates than in the solid fats, 

 which are composed more largely of palmitin and stearin. 

 Fresh animal fats are practically free from acid, while vegetable 

 oils seem to contain a small amount. 



3. Ether (Ester) Number. 



The ether number indicates the milligrams of potassium 

 hydrate required for the saponification of the neutral esters in 

 1 gram of an oil, fat or wax. 



The ether number is represented by the difference between 

 the saponification and acid numbers, and in cases where there 

 are no free fatty acids present, is identical with the saponifica- 

 tion number. 



Supplementary Notes. — Natural fats, both animal and vege- 

 table, contain practically only triglycerides, — neutral glycyl 

 esters. These glycerides may occur, however, to some extent as 

 complex molecules instead of simple. 



Lewkowitsch asserts that the presence of free fatty acids in- 

 dicates previous hydrolysis of the triglycerides, and hydrolysis 

 conditions the presence of monoglycerides and diglycerides, 

 therefore the so-called ether number loses its definite character 

 as free acids increase. 



